This invention relates to an asynchronous transfer mode (ATM) network having a network controller which controls quality of connections in the ATM network.
An ATM network of a specific type has a plurality of ATM exchangers each of which is connected to at least one of the other exchangers and to a plurality of terminal equipment units. A network controller is connected to all of the exchangers so as to control admitting and releasing connections between the terminal equipment units.
The network controller prevents or solves congestion of traffic on connections at each of the exchangers so as to keep predetermined quality of the connections.
When the network controller receives a call from one of the terminal equipment units, the network controller decides whether or not an empty bandwidth exists which is wide enough for admission of a new connection required by the call. Namely, the network controller decides whether or not the congestion is caused to occur by the admission of the new connection.
If the empty bandwidth is not wide enough, the network controller operates according to priority of the new connection. Specifically, the network controller searches connections which do not have priority over the new connection from existing connections. Then, the network controller, for example, disconnects one or more of searched connections to admit the new connection. Moreover, there is another case that the network controller limits a bandwidth of one of the searched connections so as to admit the new connection. In addition, there is still another case that the network controller discards cells which are transmitted through one of the searched connections so as to admit the new connection.
When the congestion occurs at some of the ATM exchangers, the network controller searches connections which have the lowest priority among the existing connections. Then, the network controller regulates one of the searched connections in the manner mentioned above to prevent the congestion.
Therefore, each of the existing connections is not always secured until an end of transmission in the specific type ATM network.
In addition, the bandwidth of each connection is decided by the network controller.
Therefore, the new connection is not always given the bandwidth requested by the call signal.
It is therefore an object of this invention to provide an ATM network which enables designation of a bandwidth from a terminal equipment.
It is therefore another object of this invention to provide an ATM network oaf the type described which keeps a bandwidth stable until an end of transmission.
It is therefore still another object of this invention to provide an ATM network of the type described which accomplishes stable connection quality.
Other objects of this invention will become clear as the description proceeds.
In order to understand the gist of this invention, it should be noted that an asynchronous transfer mode network has exchange, which is connected to a plurality of terminal equipment units, for admitting a connection in response to a call signal sent from one of the terminal equipment units.
According to an aspect of this invention, the asynchronous transfer mode network comprises a network controller which is connected to both the exchange and to the terminal equipment units by logic transmission line circuits for receiving the call signal and for judging whether or not the connection can be admitted in the asynchronous transfer mode network to order the exchange to admit the connection.